Field of the Invention
The invention is related to fibers, methods, and devices for collection of bioaerosols and particles on fiber structures. The invention is also related to electrospun materials for filtration and air sampling, in particular the collection of bioaerosols.
Description of the Related Art
This application is related to U.S. application Ser. No. 11/559,282, filed on Nov. 13, 2006, entitled “Particle Filter System Incorporating Nanofibers,” the entire contents of which are incorporated herein by reference. This application is related to U.S. application Ser. No. 10/819,916, filed on Apr. 8, 2004, entitled “Electrospinning of Polymer Nanofibers Using a Rotating Spray Head,” the entire contents of which are incorporated herein by reference. This application is also related to U.S. application Ser. No. 10/819,942, filed on Apr. 8, 2004, entitled “Electrospray/electrospinning Apparatus and Method,” the entire contents of which are incorporated herein by reference. This application is related to U.S. application Ser. No. 10/819,945, filed Apr. 8, 2004, entitled “Electrospinning in a Controlled Gaseous Environment,” the entire contents of which are incorporated herein by reference. This application is related to U.S. Ser. No. 11/130,269, filed May 17, 2005 entitled “Nanofiber Mats and Production Methods Thereof,” the entire contents of which are incorporated herein by reference.
Collection of both indoor and outdoor air samples is important for monitoring air quality. A wide range of microorganisms are of interest including bacteria, fungi and viruses. From a health standpoint, toxins and allergens may be of interest as well. For example see, J. M. Macher (1999) Bioaerosols, Assessment and Control, American conference of Governmental Industrial Hygienists, Cincinnati, Ohio.
More recently, concerns about airborne pathogens being present due to natural processes, accidents, or terrorist attacks has led to the need for improved sampling systems. In addition to the problem of collecting the aerosol (particles) is the problem of recovering the particles for analysis. In the case of biological particles, a common problem is that the organisms die during collection or after collection while awaiting laboratory analysis. Current sampling methods onto microbiological media do not permit extended sampling times beyond 30-45 minutes in the case where preservation of viable organisms is of interest.
In general, a concentrated, viable collect of submicrometer biological particles has been recognized in the art as a challenge. Each bioaerosol sampling method has limitations with respect to sampling time, desiccation, shelf life of sample, complexity, compatibility with analysis via PCR and live recovery. Some evaluations are given by Griffiths and Decosemo (1994); Henningson and Ahlberg (1994); Wang, Reponen et al. (2001); Tseng and Li (2005); Verreault, Moineau et al. (2008); Mainelis and Tabayoyong (2010) listed below:    Griffiths, W. D. and G. A. L. Decosemo 1994. The Assessment of Bioaerosols—a Critical-Review. Journal of Aerosol Science 25(8): 1425-1458.    Henningson, E. W. and M. S. Ahlberg 1994. Evaluation of Microbiological Aerosol Samplers—a Review. Journal of Aerosol Science 25(8): 1459-1492.    Mainelis, G. and M. Tabayoyong 2010. The Effect of Sampling Time on the Overall Performance of Portable Microbial Impactors. Aerosol Science and Technology 44(1): 75-82.    Tseng, C. C. and C. S. Li 2005. Collection efficiencies of aerosol samplers for virus-containing aerosols. Journal of Aerosol Science 36(5-6): 593-607.    Verreault, D., S. Moineau and C. Duchaine 2008. Methods for sampling of airborne viruses. Microbiology and Molecular Biology Reviews 72(3): 413-444.    Wang, Z., T. Reponen, S. A. Grinshpun, R. L. Gorny and K. Willeke 2001. Effect of sampling time and air humidity on the bioefficiency of filter samplers for bioaerosol collection. Journal of Aerosol Science 32(5): 661-674.
The collection of bioaerosols is currently performed by a number of devices that have been available for quite some time. Common bioaerosol sampling devices include:                Impactors where a jet of air deposits the bioaerosol particle on a media surface.        Impingers where the jet of air impinges on a surface within a liquid filled container.        Filters where the particles are collected on the surface of the filter.        
Impactors are limited with respect to sampling time because the collection media used to enumerate the number of colonies of organisms for viability after collection is subject to desiccation, thus limiting the sampling time. Also typical impactors designed for microorganisms have a lower particle size collection limit of about 0.5 micrometers. (Anderson, A. A. (1958) New sampler for collection, sizing, and enumeration of viable airborne particles, J. Bacteriol. 76, 471-484)
Impingers are limited in their sampling time from the evaporation of the collecting fluid. The collection efficiency is dependent on the volume of fluid in the impinger. Also the microorganisms may be lost by reaerosolization from the fluid during sampling (Grinshpun, S. A., K. Willeke, V. Ulevicius, A. Juozaitis, S. Terzieva, J. Gonnelly, G. N. Stelma and K. P. Brenner (1997) Effect of impaction, bounce and reaerosolization on the collection efficiency of impingers. Aerosol Sci. Technol. 26, 326-342).
Filters and other collection media such as membranes have long been used to trap aerosol and bioaerosols for subsequent analysis thereof. Filters with a poor figure of merit or quality at least require higher pressures to force air flow through. An example consequence is that in portable samplers operation is severely limited due to battery life in the samplers with filters with high pressure drop. Filter figure of merit or quality is defined as FoM=−log(Pt)/ΔP, where Pt is the penetration of particle at a specific size through the filter and ΔP is the pressure drop at a specific gas flow rate. The larger the FoM, the better will be the performance of the filter. See Hinds, W. C. (1982) Aerosol Technology, Wiley, New York, N.Y.). Further, the flow of air through the filters or membranes after a biological aerosol has been trapped can lead to the desiccation of the medium about the bioaerosol and death of the bioaerosol.
Thus, in general, a list of existing air sampling technologies for bioparticles and their drawbacks are provided below.
Typical longestSamplerd50sampling timeNotesImpinger~0.3 μm30minGood for shorte.g. AGI-30term samplingImpactor~0.7 μm20minCollection one.g. Andersonagar reducesdesiccationSKC~0.3 μm8hrsFluid for longBioSamplerterm samplinginterferes withPCRFiltration*60min†Desiccation is ae.g. 37-mmsignificantcassette withproblem withNucleoporefiltration* Filtration has a most penetrating size about 0.1 to 0.3 μm with efficiency of collection typically high (>80%) across size range.†Longer term sampling is possible but organisms do not survive.